Optical and capacitance type, phase transition, humidity-respons

Details Optical and capacitance type, phase transition, humidity-respons Optical and capacitance type, phase transition, humidity-respons

1990-08-02

1992-01-21

Maples, John S.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, 252963, C09K 1932, C09K 1952

Patent

active

050825887

ABSTRACT:
The invention provides novel chemical compositions for use in primary, optical/capacitance hygrometric devices. It also provides methods for using these compositions as sensors for the precise measurement of the humidity of gases as well as the apparatus. The chemical compositions, which of themselves sense the change in water vapor pressure, are birefringent, translucent, and anisotropic at a first water vapor pressure/temperature, but non-birefrigent, optically clear, and isotropic at a second vapor pressure/temperature. Optical changes which accompany these phase changes may be amplified. Some compositions, exhibit abrupt and large increases in their dielectric constant coincident with the optical changes which occur at the phase shift point. Others show a large and precisely linear change in dielectric contant over many decades of relative humitity (RH), but the optical shift occurs at a precise point within the range. By noting the capacitance readout from a prestandardized combination optical/capacitance hygrometric device at the moment of optically indicated phase shift (when the system changes from isotropic to birefringent), any drift in the electronics of the device can be immediately detected since the sensor's phase shift point is invariant. If it is desired to eliminate polarizer amplifiers because of their cost, sensor substrates can be shaped so that internal reflection within the substrate and optical coupling of the birefringent sensor to the substrate generate excellent optical signals at the sensor's trigger points. The devices and methods of the new hygrometry allow many variations on the primary requirements. If desire, the sensor can be made an integral part of a capacitance-sensitive IC.

REFERENCES:
patent: 3776038 (1973-12-01), Elliott
patent: 4166891 (1979-09-01), Elliott
patent: 4175207 (1979-11-01), Elliott
patent: 4292162 (1981-09-01), Ambler
patent: 4786331 (1988-11-01), Ueda et al.
patent: 4849345 (1989-07-01), Asano et al.
patent: 4909986 (1990-03-01), Kobayashi et al.

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